The organic electroluminescence (EL) device using organic material has been considered to be hopeful for use as a solid emitting type full color display device, which is cheap and has a large area and accordingly, there have widely been conducted a variety of investigations for the development of such devices. In general, the EL device comprises a emitting layer and a pair of electrodes interposing the emitting layer between them. The emission of light from the EL device is such a phenomenon that, when an electric field is applied between these electrodes, electrons are injected into the emitting layer from the side of the cathode, while holes are likewise injected into the layer from the side of the anode, subsequently the electrons are recombined with the holes within the emitting layer to generate excited states and energies are converted in the form of light when the excited states are brought back to the ground states.
Recently, the techniques relating to the organic EL device have made a considerable progress. The organic EL device can be characterized in that it can be formed into a thin and light-weight emitting device which has a high-luminance even when applying a low voltage and a wide range of luminous wavelengths, and which device can respond at a high speed and thus said characteristics suggest a wide range of possible applications of the organic EL device.
However, the organic EL device at present is needed to have a higher luminance of a light output or higher conversion efficiency. In addition, the existing organic EL device has still suffered from a variety of problems concerning the durability such as a change of in characteristics with time when using the device over a long period of time deterioration due to an atmospheric gas containing oxygen or a moisture. Furthermore, the EL device should emit blue, green, and red light excellent in the purity of color when taking into consideration the application thereof to the full color display devices or the like, but this problem has not yet been solved satisfactorily.
JP2005-514739A discloses an example in which a compound having a dibenzoquinoxaline skeleton is used as a material for a hole blocking layer (electron transporting layer) and an emitting material. However, this patent application does not sufficiently disclose the characteristic properties of the device and accordingly, the effect accomplished by the device is vague.
Japanese Patent No. 3,571,977 discloses an organic EL device which makes use of a hexaazatriphenylene derivative as a material for an electron injecting layer. This EL device is improved in the electron injecting properties, but the improvement has not yet been sufficient.
Moreover, there have been known, as materials for electron injecting layers, oxadiazole derivatives such as those disclosed in, for instance, Japanese Un-Examined Patent Publication (Hereunder simply referred to as “J.P. KOKAI”) Nos. Hei 2-216791 and Hei 4-363891; and triazine derivatives such as those disclosed in, for instance, J.P. KOKAI Nos. Hei 7-41759 and Hei 7-90260. However, the organic emitting devices prepared using these materials have still been insufficient in their stability of films, and their electron injection efficiencies and thus these devices have still been insufficient in the luminance of the emitted light and the lifetime.
Japanese Patent No. 3,614,405 discloses an organic EL device which comprises hexaazatriphenylene derivative having 6 cyano substituents. When this compound is used in the hole injecting layer, the resulting device is improved in the hole injecting property and said improvement contributes to the reduction of the operating voltage of the device. However, since the intermolecular interaction due to polar functional groups is too strong, the vapor deposition temperature of the compound becomes high and thus there is concern that the compound may undergo decomposition.    [Patent Document 1] JP2005-514739A;    [Patent Document 2] Japanese Patent No. 3,571,977;    [Patent Document 3] J.P. KOKAI Hei 2-216791;    [Patent Document 4] J.P. KOKAI Hei 4-363891;    [Patent Document 5] J.P. KOKAI Hei 7-41759;    [Patent Document 6] J.P. KOKAI Hei 7-90260;    [Patent Document 7] Japanese Patent No. 3,614,405.